Suppression of monocyte and neutrophil function by recombinant IL-2

Little IS known about the influence of IL-2 on phagocytes. We now describe the effects of human recombinant IL-2 on human neutrophil and monocyte functions related to mobility, phagocytosis, glucose uptake, respiration and degranulation. Neutrophil adherence and hexose monophosphate shunt activities were both suppressed after incubation with IL-2. IL-2 had no effect on neutrophil migration, phagocytosis, deoxyglucose uptake or degranulation, ionocytes demonstrated a greater sensitivity to IL-2 with suppression of monocyte adherence, random and stimulated migration, glucose uptake and hexose monophosphate shunt activity, even after addition of phorbol myristate acetate. Monocyte phagocytosis and degranulation were not affected. All of the effects observed were dose-dependent within a biologically active range for IL-2. These studies suggest that IL-2 may have an important down-regulatory role across a broad range of monocyte functions including movement, deoxyglucose uptake and respiration. However, its role in regulation of neutrophil function is limited to adherence and respiration. IL-2 may be a more versatile cytokine than has previously been appreciated

Finite element simulation of plates under non-uniform blast loads using a point-load method: Blast wave clearing

There are two primary challenges associated with assessing the adequacy of a protective structure to resist explosive events: firstly the spatial variation of load acting on a target must be predicted to a sufficient level of accuracy; secondly, the response of the target to this load must also be quantified. If a target is embedded within a finite reflecting surface then the process of blast wave clearing will occur. Diffraction of the blast around the target edge causes a low pressure relief wave to propagate inwards towards the centre of the target, reducing the late-time development of pressure and resulting in high spatial non-uniformity of the blast load. This paper presents experimental measurements of the dynamic displacement-time histories of steel plates subjected to blast loads where the plate was situated within a finite reflecting surface to allow for clearing effects to take place. Associated finite element modelling is presented, where coupled blast-target interaction is modelled explicitly using the Arbitrary Lagrangian-Eulerian solver in LS-DYNA. An alternative method is presented, where the loading is applied as discrete load predictions at individual nodes. The results show that vast computational savings can be made when modelling the load in this manner, as well as better agreement with the experimental measurements owing to a more accurate representation of the applied load

Displacement timer pins: An experimental method for measuring the dynamic deformation of explosively loaded plates

The measurement of dynamic deformation of an explosively loaded plate is an extremely onerous task. Existing techniques such as digital image correlation are expensive and the equipment may be damaged by explosively driven debris/ejecta, particularly if it is necessary to locate such equipment close to loaded elements which are likely to fail. A new, inexpensive and robust measurement technique for use in full-scale blast testing is presented, which involves the placement of displacement timer pins (DTPs) at pre-defined distances from the rear surface of the centre of a plate. A strain gauge on the perimeter of each pin records the time at which the plate comes into contact with the end of each DTP and hence has deformed to that value of displacement, giving a direct measure of the time-varying deformation at a discrete point on the plate. An experimental proof-of-concept was conducted and the results are compared with numerical displacements determined using LS-DYNA. The numerical and experimental results were in very good agreement, which suggests that the proposed experimental method offers a valuable means for determining the full-scale response of structures subjected to blast loads in aggressive environments. Further improvements to the experimental procedure are outlined, along with applications where the DTPs are particularly suited. 2015 Elsevier Ltd. All rights reserved

Effects of strain rate and moisture content on the behaviour of sand under one-dimensional compression

The influence of strain rate and moisture content on the behaviour of a quartz sand was assessed using high-pressure quasi-static (0.001 /s) and high-strain-rate (1000 /s) experiments under uniaxial strain. Quasi-static compression to axial stresses of 800 MPa was carried out alongside split Hopkinson pressure bar (SHPB) experiments to 400 MPa, where in each case lateral deformation of the specimen was prevented using a steel test box or ring, and lateral stresses were recorded. A significant increase in constrained modulus was observed between strain rates of 0.001 /s and 1000 /s, however a consistently lower Poisson's ratio in the dynamic tests minimised changes in bulk modulus. The reduction in Poisson’s ratio suggests that the stiffening of the sand in the SHPB tests is due to additional inertial confinement rather than an inherent strain-rate dependence. In the quasi-static tests the specimens behaved less stiffly with increasing moisture content, while in the dynamic tests the addition of water had little effect on the overall stiffness, causing the quasi-static and dynamic series to diverge with increasing moisture content

Experimentation and modelling of near field explosions

Repeatable experimental results and numerical work has shown that using the Jones-Wilkins-Lee (JWL) equation of state (EOS) will give very accurate results of peak pressures and impulse delivered to a rigid target at large scaled distances. However, recent experiments/numerical modelling at small scaled distances show that the JWL will overpredict peak pressures and impulse due to the assumption of (near) instantaneous energy release from detonation. The results of this experimental/numerical study are presented herein. In the experimental work PE4 spheres at two different scaled distances have been tested using an array of Hopkinson Pressure Bars (HPB) at specific points on a rigid target to measure the local pressure-time histories. From the HPB measurements, it appears that below certain scaled distances there are chemical-physical mechanisms that do not have sufficient time to contribute to the energy driving the loading mechanisms, explaining the over-prediction of the JWL. Importantly though, the experimental results show that at very small scaled distances (0.172 m/kg1/3) the test to test percentage variation is very low (5.1%); whilst at larger scaled distances (0.819 m/kg1/3) it is much higher (23.1%). This paper presents a model which describes the process by which experimental results move from repeatable to variable to repeatable as scaled distance increases from the extreme near field to far field

Experimental studies of the effect of rapid afterburn on shock development of near-field explosions

Many conventional high explosives do not contain sufficient internal oxygen to fully combust the gaseous products which result from detonation of the explosive material. Because of this, under-oxygenated explosives continue to burn after detonation. This process, called afterburn, is known to influence the late-time pressure and energy released by the explosive, which has particular significance for confined explosives. Recent experimental work at the University of Sheffield, along with a small number of previous studies, has shown that some afterburn occurs at timescales commensurate with the development of the shock wave. This article presents the results from a series of tests measuring the reflected pressure acting on a rigid target following the detonation of small explosive charges. High-speed video is used to capture the emerging structure of the detonation products and air shock, while the spatial and temporal distributions of the reflected pressure are recorded using an array of 17 Hopkinson pressure bars set flush with an effectively rigid target. Tests are conducted in inert atmospheres and oxygen-rich atmospheres in order to assess the contribution of rapid afterburn on the development of the shock front and interaction with a rigid target situated close to the explosive charge. The results show that early-stage afterburn has a significant influence on the reflected shock parameters in the near-field

Repeatability of buried charge testing

The relationship between the geotechnical parameters and the impulse delivered by a charge buried shallowly (<100 mm) within a soil mass has received much attention in recent times. It has previously been demonstrated that for uniform soils a high degree of repeatability in the delivered impulse can be achieved when carefully controlling the geotechnical conditions. In this paper the authors explore the recommendations given in AEP55 regarding the testing of surrogate mine blasts using both minepots and the STANAG standard sandy gravel. With moisture content and bulk density being intrinsically coupled, using bulk density as a measure of geotechnical control and hence repeatability is questionable. A methodology for the careful preparation of the Stanag sandy gravel soil is presented along with comparative results from minepots demonstrating the comparative repeatability of both methodologies. These results are then compared with a number of other soils to allow gen-eral conclusions about the repeatability of specific soil characteristics to be drawn

Reflected pressures from explosives buried in idealised cohesive soils

Recent work has concentrated on the characterisation of the temporal and spatial impulse distribution of blast form buried charges. A new soil container preparation methodology has been created to allow for the generation of highly repeatable, tightly controlled clay beds which will allow clays of different undrained strengths to be generated. Tests using these well controlled beds has allowed for an improved understanding into which geotechnical parameters govern the impulse delivered by a buried charge. Namely in the current programme of work this is an investigation into the ‘undrained strength’ of a cohesive material as an indicator of potential impulse output. Initial results are compared against previously published work on cohesionless soils (sands) to try to establish the full range of loading which can be generated by a buried charge

Predicting the role of geotechnical parameters on the output from shallow buried explosives

Experiments have been conducted to quantify the effect the geotechnical conditions surrounding a buried charge have on the resulting output. From the results obtained the critical importance of moisture content in governing the magnitude of impulse delivered is highlighted. This has led to the development of a first-order predictive model for the impulse delivered from a buried charge, based on bulk density and moisture content, allowing rapid assessment of the effect of varying the geotechnical conditions. The work utilised a half-scale impulse measurement apparatus which incorporated a deformable target plate. Impulse, peak and residual target deflections were recorded for each test. No variations the charge geometry, mass of explosive, burial depth or stand-off were considered, with the focus solely being on the effect of the geotechnical conditions on the magnitude of loading and structural response. Five different types or grades of soils were used in the work, with both cohesive and cohesionless soils represented. The effect of air voids on the impulse generated was also investigated which showed that while strongly correlated, air voids alone is a poorer predictor of impulse than moisture content

Influence of particle size distribution on the blast pressure profile from explosives buried in saturated soils

The spatial and temporal distribution of pressure and impulse from explosives buried in saturated cohesive and cohesionless soils has been measured experimentally for the first time. Ten experiments have been conducted at quarter-scale, where localised pressure loading was measured using an array of 17 Hopkinson pressure bars. The blast pressure measurements are used in conjunction with high-speed video filmed at 100,000 fps to investigate in detail the physical processes occurring at the loaded face. Two coarse cohesionless soils and one fine cohesive soil were tested: a relatively uniform sand, a well-graded sandy-gravel, and a fine-grained clay. The results show that there is a single fundamental loading mechanism when explosives are detonated in saturated soil, invariant of particle size and soil cohesion. It is also shown that variability in localised loading is intrinsically linked to the particle size distribution of the surrounding soil